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Difficulty: HardOxygen, Ozone, and Classification of Oxides

An unknown solid metallic oxide XX dissolves in cold dilute tetraoxosulfate(VI) acid (H2SO4\text{H}_2\text{SO}_4) to form a solution that turns acidified potassium iodide (KI\text{KI}) solution brown due to the liberation of iodine, without releasing any gas during the reaction. In contrast, lead(IV) oxide (PbO2\text{PbO}_2) treated with cold dilute acid does not produce hydrogen peroxide (H2O2\text{H}_2\text{O}_2). Which of the following correctly classifies oxide XX and accounts for its distinct behavior from lead(IV) oxide?

  1. Oxide XX is a peroxide containing the O22−\text{O}_2^{2-} ion which yields H2O2\text{H}_2\text{O}_2 with dilute acid, whereas PbO2\text{PbO}_2 is a dioxide containing simple O2−\text{O}^{2-} ions.Answer
  2. B
    Oxide XX is an amphoteric oxide that oxidizes iodide ions, whereas PbO2\text{PbO}_2 is a purely basic oxide that cannot participate in redox reactions.
  3. C
    Oxide XX is an allotrope of oxygen, whereas PbO2\text{PbO}_2 is a neutral oxide.
  4. D
    Oxide XX is a basic oxide because it reacts with acid without gas evolution, whereas PbO2\text{PbO}_2 is an acidic oxide.

Answer

Oxide X is a peroxide containing the O22−\text{O}_2^{2-} ion which yields H2O2\text{H}_2\text{O}_2 with dilute acid, whereas PbO2\text{PbO}_2 is a dioxide containing simple O2−\text{O}^{2-} ions.
Peroxides (such as sodium peroxide or barium peroxide) contain the peroxide ion O22−\text{O}_2^{2-} with oxygen in the −1-1 oxidation state. When treated with cold dilute acids, they form hydrogen peroxide (H2O2\text{H}_2\text{O}_2), which oxidizes I−\text{I}^- to brown I2\text{I}_2. In contrast, dioxides like lead(IV) oxide (PbO2\text{PbO}_2) contain standard oxide ions (O2−\text{O}^{2-}) with lead in the +4+4 oxidation state, so they do not produce H2O2\text{H}_2\text{O}_2 under cold dilute acid conditions.

Step-by-Step Solution

1
Analyze the chemical test result for Oxide X.
Oxide XX reacts with cold dilute H2SO4\text{H}_2\text{SO}_4 to form a solution that oxidizes KI\text{KI} to I2\text{I}_2 (brown solution).
This behavior is characteristic of peroxides (such as Na2O2\text{Na}_2\text{O}_2 or BaO2\text{BaO}_2), which react with dilute acids to produce hydrogen peroxide (H2O2\text{H}_2\text{O}_2). Hydrogen peroxide is a powerful oxidizing agent that liberates iodine from acidified potassium iodide: H2O2+2H++2I−→2H2O+I2\text{H}_2\text{O}_2 + 2\text{H}^+ + 2\text{I}^- \rightarrow 2\text{H}_2\text{O} + \text{I}_2.
2
Distinguish between peroxides and dioxides.
Peroxides contain the peroxide linkage [−O−O−]2−[-\text{O}-\text{O}-]^{2-} (O22−\text{O}_2^{2-} ion with oxygen in oxidation state −1-1), while true dioxides contain O2−\text{O}^{2-} ions with the metal in oxidation state +4+4.
Dioxides like PbO2\text{PbO}_2 and MnO2\text{MnO}_2 do not contain peroxide ions and therefore do not form H2O2\text{H}_2\text{O}_2 when treated with cold dilute acids.
3
Select the correct classification matching the observed chemistry.
Oxide XX is a peroxide, whereas PbO2\text{PbO}_2 is a dioxide.
This structural difference explains why oxide XX yields H2O2\text{H}_2\text{O}_2 capable of liberating iodine from KI\text{KI}, while PbO2\text{PbO}_2 does not.

Key Concept

Distinction between peroxides (containing O22−\text{O}_2^{2-}) and dioxides (containing O2−\text{O}^{2-}) based on acid reactions and peroxide test
Estimated Time:2m 0s
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Topics

Oxygen, Ozone, and Classification of Oxides

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